Composition for bonded magnets and method of manufacturing the same

ABSTRACT

The present invention relates to a composition for bonded magnets having good hot water resistance and a method of manufacturing the composition. The method of manufacturing a composition for bonded magnets includes: obtaining a first kneaded mixture by kneading a rare earth-iron-nitrogen-based magnetic powder and an acid-modified polypropylene resin; and obtaining a second kneaded mixture by kneading the first kneaded mixture with a polypropylene resin and an amorphous resin having a glass transition temperature of 120° C. or higher and 250° C. or lower, wherein, with respect to 100 parts by weight of the rare earth-iron-nitrogen-based magnetic powder, the amount of the acid-modified polypropylene resin is 3.5 parts by weight or greater and less than 10.4 parts by weight, and the total amount of the polypropylene resin and the amorphous resin is 0.35 part by weight or greater and less than 3.88 parts by weight.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to Japanese Patent Application No.2017-140843 filed on July 20, 2017 and Japanese Patent Application No.2018-127536 filed on Jul. 4, 2018. The disclosures of Japanese PatentApplication No. 2017-140843 and Japanese Patent Application No.2018-127536 are hereby incorporated by reference in their entireties.

BACKGROUND Technical Field

The present invention relates to a composition for bonded magnets and amethod of manufacturing the composition.

Description of Related Art

High-performance small motors and actuators for use in engine rooms inautomobiles are required to provide many high-level functions, such asvery high magnetic force, heat resistance, and corrosion resistance.Thus, rare earth sintered magnets have been mainly used for such motorsand actuators. However, along with the recent demand for reduction inweight and cost, rare earth sintered magnets have been increasinglyreplaced by rare earth bonded magnets which are less expensive materialsthan rare earth sintered magnets and which have high flexibility inshape, high dimensional stability, and low production cost. Inparticular, rare earth bonded magnets in which rareearth-iron-nitrogen-based magnetic powders (nitride powders), amongother rare earth magnetic powders, are dispersed in resinscharacteristically have good corrosion resistance. Thus, they can beexpected to be applicable to small motors and actuators for use undersevere conditions, such as immersion in hot water or exposure tohigh-temperature, high-humidity environments.

Mainly, 12 nylon resins (hereinafter, PA12 resins) or polyphenylenesulfide resins (hereinafter, PPS resins) are used as resin binders ofrare earth-iron-nitrogen-based bonded magnets. PA12 resins are mostcommonly used binders because they have various features such as goodmechanical strength, fluidity, magnetic powder filling properties, andrecycling properties. However, since PA12 resins have a relatively highwater absorption rate due to the presence of amide groups in thestructure, they can undergo dimensional changes due to water absorptionand a reduction in strength due to hydrolysis when they are exposed tosevere environments such as immersion in hot water. Although PPS resinsare poor in mechanical strength and magnetic powder filling propertiesas compared to PA12 resins, they have very good heat resistance andwater resistance and thus are used as binders for bonded magnets for usein severe environments. However, these PPS resins have a high meltingpoint (about 280° C.), and thus the temperature needs to be high (over300° C.) for kneading these resins with magnetic powders. Rareearth-iron-nitrogen-based magnetic powders, which have high surfaceactivity, can be oxidatively degraded when kneaded with PPS resins athigh temperatures, resulting in a reduction in long-term magnetic forcestability (demagnetization resistance).

Polypropylene resins may be used as alternative resins to PA12 and PPSresins. Polypropylene resins have water resistance but have a lowpolarity and thus are poor in adhesion to magnetic powders and thereforein magnetic powder filling properties and mechanical strength. Inaddition, these polypropylene resins have a low glass transitiontemperature (Tg=about 0° C.), and the molecules can be excited as thetemperature increases, which unfortunately results in lower waterresistance. These resins are difficult to use under severe conditions,such as immersion in hot water (e.g. at 100° C. or higher) or exposureto high-temperature, high-humidity environments.

In regard to these problems, JP 2007-149911 A discloses, instead ofbonded magnets using rare earth-iron-nitrogen-based magnetic powders, apermanent magnet in which the surface of a permanent magnet body iscovered with a packing sheet including a stack of a heat-adhesive resinlayer formed from an acid-modified polyolefin or the like and aheat-resistant resin layer formed from a biaxially stretchedpolyethylene naphthalate or the like.

SUMMARY

According to embodiments, the present invention aims to provide acomposition for bonded magnets for producing a bonded magnet having goodhot water resistance, and a method of manufacturing the composition.

Specific means to solve the problems are as described below and thepresent invention encompasses the following embodiments.

According to a first embodiment of the present invention, a method ofmanufacturing a composition for bonded magnets includes: obtaining afirst kneaded mixture by kneading a rare earth-iron-nitrogen-basedmagnetic powder and an acid-modified polypropylene resin; and obtaininga second kneaded mixture by kneading the first kneaded mixture with apolypropylene resin and an amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower, wherein, withrespect to 100 parts by weight of the rare earth-iron-nitrogen-basedmagnetic powder, an amount of the acid-modified polypropylene resin is3.5 parts by weight or greater and less than 10.4 parts by weight, and atotal amount of the polypropylene resin and the amorphous resin is 0.35part by weight or greater and less than 3.88 parts by weight.

According to a second embodiment of the present invention, a method ofmanufacturing a composition for bonded magnets includes: providing arare earth-iron-nitrogen-based magnetic powder having a coat layercontaining a basic group, an acid-modified polypropylene resin, apolypropylene resin, and an amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower; and obtaining akneaded mixture by kneading the rare earth-iron-nitrogen-based magneticpowder having a coat layer containing a basic group, the acid-modifiedpolypropylene resin, the polypropylene resin, and the amorphous resinhaving a glass transition temperature of 120° C. or higher and 250° C.or lower, wherein, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, an amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and a total amount of the polypropyleneresin and the amorphous resin is 0.35 part by weight or greater and lessthan 3.88 parts by weight.

According to a third embodiment of the present invention, a compositionfor bonded magnets contains: a rare earth-iron-nitrogen-based magneticpowder; an acid-modified polypropylene resin; a polypropylene resin; andan amorphous resin having a glass transition temperature of 120° C. orhigher and 250° C. or lower, wherein, with respect to 100 parts byweight of the rare earth-iron-nitrogen-based magnetic powder, an amountof the acid-modified polypropylene resin is 3.5 parts by weight orgreater and less than 10.4 parts by weight, and a total amount of thepolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight.

According to the above embodiments, it is possible to provide acomposition for bonded magnets for producing a bonded magnet having goodhot water resistance, and methods of manufacturing the composition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the relationships between the exposure time and thedemagnetization ratio in a pressure cooker test (121° C./2 atm)according to Examples 1 and 9 and Comparative Examples 1-4 of thepresent disclosure.

FIG. 2 shows the relationships between the amount of a polypropyleneresin having a number average molecular weight of 9,000 or less and thedemagnetization ratio after a pressure cooker test (121° C./2 atm/450hr) according to Examples 1 to 7 of the present disclosure.

FIG. 3 shows the relationship between the degree of maleic anhydridemodification of an acid-modified polypropylene resin and thedemagnetization ratio after a pressure cooker test (121° C./2 atm/200hr) according to Example 1 of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, certain embodiments of the present invention will bedescribed. The embodiments described below are intended to give aconcrete form to the technical idea of the present invention and are notintended to limit the scope of the present invention to the embodimentsdescribed below. When multiple substances correspond to a componentincluded in a composition, “the amount of the component in thecomposition” as used in the present specification refers to the totalamount of the multiple substances in the composition, unless otherwisestated.

Method of Manufacturing Composition for Bonded Magnets According toFirst Embodiment

The manufacturing method according to this embodiment includes:obtaining a first kneaded mixture by kneading a rareearth-iron-nitrogen-based magnetic powder and an acid-modifiedpolypropylene resin; and obtaining a second kneaded mixture by kneadingthe first kneaded mixture with a polypropylene resin and an amorphousresin having a glass transition temperature of 120° C. or higher and250° C. or lower. With respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, the amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and the total amount of thepolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight.

Polypropylene resins have water resistance, but these resins are poor inadhesion to metals due to their low polarity and also have insufficientheat resistance. Amorphous resins are suitable for compositions forbonded magnets because the degree of mold shrinkage of these resins issmaller than that of crystalline resins; however, since these amorphousresins have high viscosity, the kneading temperature during themanufacture of a composition for bonded magnets needs to be set higherthan the glass transition temperature at which the resins start to melt.This may cause oxidative degradation of the rareearth-iron-nitrogen-based magnetic powder used, depending on the type ofresin. Thus, this embodiment includes obtaining a first kneaded mixtureby kneading a rare earth-iron-nitrogen-based magnetic powder and anacid-modified polypropylene resin, in order to provide increased waterresistance due to the nature of polypropylene resins and increasedadhesion to the magnetic powder due to the presence of the acid-modifiedportion of the resin. Subsequently, this embodiment includes obtaining asecond kneaded mixture by kneading the first kneaded mixture with apolypropylene resin and an amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower at a predeterminedratio with respect to the magnetic powder, in order to provide thebonded magnet with hot water resistance attributable to thepolypropylene resin and the amorphous resin. Moreover, kneading thepolypropylene resin and the amorphous resin together reduces theviscosity, which allows the kneading temperature during the manufactureof a composition for bonded magnets to be set close to the glasstransition temperature of the amorphous resin. Specifically, it isconsidered that, when the amorphous resin has a glass transitiontemperature of 120° C. or higher, the amorphous resin maintains thermalstability even in an environment at 120° C., and therefore the bondedmagnet provides hot water resistance in addition to water resistanceattributable to polypropylene. It is also considered that, when theamorphous resin has a glass transition temperature of 250° C. or lower,the kneading temperature during the manufacture of a composition forbonded magnets is allowed to be set to 250° C. or lower where themagnetic powder is less likely to undergo oxidative degradation, andtherefore the bonded magnet has improved hot water resistance.

The steps are described in detail below.

Obtaining First Kneaded Mixture

The first kneaded mixture may be obtained by kneading a rareearth-iron-nitrogen-based magnetic powder and an acid-modifiedpolypropylene resin while heating at 210° C. to 250° C. Any kneadingmachine may be used, and examples include single-screw extruders,special single-screw extruders, kneaders, mixing rollers, Banburymixers, intermeshing type twin-screw extruders, and non-intermeshingtype twin-screw extruders.

Rare Earth-Iron-Nitrogen-Based Magnetic Powder

Examples of the rare earth-iron-nitrogen-based magnetic powder includeSmFeN-based magnetic powders having good remanence and good inherentcoercive force. The SmFeN-based magnetic powder may be a nitridecontaining a rare earth metal (Sm), iron (Fe), and nitrogen (N) asrepresented by general formula: Sm_(x)Fe_((100-x-y))N_(y), where thevalue “x” indicating the atomic percent (%) of the rare earth metal Smis in a range of 3 to 30 (at %); the value “y” indicating the atomicpercent (%) of N is in a range of 5 to 15 (at %); and the balance ismainly Fe. The reason for limiting the atomic percent of Sm to 3 to 30(at %) is as follows: at less than 3 at %, separation of the α-Fe phasemay occur, thereby reducing the coercive force of the nitride so thatthe magnet can become unpractical; and at greater than 30 at %,precipitation of Sm may occur, rendering the alloy powder unstable inthe air and thus reducing remanent magnetization. Meanwhile, the reasonfor limiting the atomic percent of nitrogen N to 5 to 15 (at %) is asfollows: at less than 5 at %, coercive force may is hardly exerted; andat greater than 15 at %, nitrides of Sm, iron, or alkaline metalsthemselves may be formed.

The SmFeN-based magnetic powder may be manufactured, for example, by amethod disclosed in Japanese Patent No. 3698538. The SmFeN-basedmagnetic powder may have an average particle size of 2 μm to 5 μm and astandard deviation of the particle size distribution of 1.5 or less.

The magnetic powder to be used in this embodiment is preferablysurface-treated in order to improve oxidation resistance, waterresistance, resin wettability, or chemical resistance as describedbelow. Such treatments may be used in combination, if necessary. Thesurface treatment may be performed by a process chosen according to theneeds, but basically by a wet process or a dry process (e.g. using amixer).

Examples of such treatment agents include, firstly, phosphorus compoundshaving a P—O bond. Examples of phosphoric acid treatment agents includeinorganic or organic phosphoric acid treatment agents such asorthophosphoric acid, sodium dihydrogen phosphate, ammonium dihydrogenphosphate, diammonium hydrogen phosphate, zinc phosphate, calciumphosphate, and other phosphates; hypophosphorous acid andhypophosphites; pyrophosphoric acid, and polyphosphoric acids.Basically, such a phosphoric acid source may be dissolved in water or anorganic solvent such as IPA and optionally supplemented with a reactionaccelerator such as nitric acid ions and/or a crystal grain refiningagent such as V ions, Cr ions, or Mo ions, and then a magnetic powdermay be introduced into the resulting phosphoric acid bath to form apassivation film having a P-O bond on the surface of the powderparticles.

Besides these phosphate film treatments, the following methods may beused: treatments in which submicron or nano-order particles are adsorbedto the magnetic powder surface by a wet or dry process to form aninorganic oxide film such as silica, alumina, or titania film; sol-gelmethods using organic metals; or treatments in which an inorganicoxide-treated film is formed on the magnetic powder surface.

Next, a coating treatment of a magnetic powder with a coupling agent isdescribed. Before kneading the resin and the magnetic powder to form acomposite, a coat layer may be formed on the outermost surface of thesurface-treated-film of the magnetic powder using a coupling agent inorder to provide compatibility and association with the resin. It ispreferable to form a coat layer using a coupling agent having a basicgroup in order to provide association with the acid-modified portion ofthe acid-modified polypropylene resin. Examples of the basic groupinclude epoxy and amino groups. It is preferable in view of associationto use a coupling agent having an amino group. Examples of silanecoupling agents having an amino group includeγ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropyltriethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane,γ-aminopropyltriethoxysilane, γ-aminopropylmethyldiethoxysilane,N-phenyl-γ-aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropylmethyldimethoxysilane,N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilanehydrochloride, N-β(aminoethyl)-γ-}aminopropyltrimethoxysilane,N-β(aminoethyl)-γ-aminopropylmethyldimethoxysilane,bis(trimethoxysilylpropyl)amine, andN-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine. In thepresent invention, it is preferable to use a coupling agent having goodreactivity with the acid anhydride group attached to the resin,preferably, for example, γ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropyltriethoxysilane,γ-aminopropyltrimethoxysilane, or γ-aminopropyltriethoxysilane.

Moreover, in order to obtain a molded magnet having good properties, theamount (by weight) of amino groups derived from the coupling agent perunit surface area of the magnetic powder is more preferably 0.5 to 5mg/m². An amount of less than 0.5 mg/m² may result in insufficientinsulation between the particles. An amount of greater than 5 mg/m² mayresult in both lower magnetic properties and lower water resistance dueto agglomeration of the magnetic particles resulting from excessivelyincreased affinity between these particles.

Acid-Modified Polypropylene Resin

In order to increase the adhesion to the rare earth-iron-nitrogen-basedmagnetic powder, it is preferable to use an acid-modified polypropyleneresin. Examples of the acid include saturated or unsaturated carboxylicacids and carboxylic acid anhydrides. Specific examples include maleicacid, fumaric acid, succinic acid, oxalic acid, maleic anhydride, andsuccinic anhydride. Among these, maleic anhydride is preferable in viewof association with the rare earth magnetic powder. Examples of maleicanhydride-modified polypropylene resins include maleic anhydride-graftedpolypropylene resins. The maleic anhydride group may further increaseadhesion by chemically bonding to the basic group at the tip of thecoupling agent, particularly having an amino group, on the outermostsurface of the magnetic powder. The maleic anhydride-modifiedpolypropylene resins are polypropylene resins modified with maleic acidor maleic anhydride. Such modification may be carried out byconventionally known methods. For example, maleic anhydride may be addedtogether with a peroxide to a polypropylene resin and kneaded using asingle screw kneading extruder or a twin-screw kneading extruder tocause a graft reaction. The maleic anhydride-modified polypropyleneresin to be used in the bonded magnet according to this embodiment maybe produced by modifying a commercially available polypropylene resinwith an acid anhydride by a method as described above. Alternatively, itmay be a commercially available maleic anhydride-modified polypropyleneresin.

The degree of acid modification relative to polypropylene is, forexample, in a range of 0.1% by weight or greater and 5% by weight orless, preferably of 0.2% by weight or greater and 2.8% by weight orless, more preferably of 0.35% by weight or greater and 1.4% by weightor less, particularly preferably of 0.7% by weight or greater and 1.25%by weight or less, to improve hot water resistance.

The number average molecular weight of the acid-modified polypropyleneresin is preferably in a range of 20,000 or greater and 90,000 or less.A number average molecular weight of less than 20,000 reduces themechanical strength of the bonded magnet. A number average molecularweight of greater than 90,000 increases the viscosity.

The amount of the acid-modified polypropylene resin is, for example, ina range of 3.5 parts by weight or greater and less than 10.4 parts byweight, preferably of 4 parts by weight or greater and less than 9.3parts by weight, particularly preferably of 5 parts by weight or greaterand 7 parts by weight or less, with respect to 100 parts by weight ofthe rare earth-iron-nitrogen-based magnetic powder. An amount of lessthan 3.5 parts by weight reduces the adhesion to the rareearth-iron-nitrogen-based magnetic powder. An amount of 10.4 parts byweight or greater reduces hot water resistance.

Obtaining Second Kneaded Mixture

The second kneaded mixture may be obtained by kneading the first kneadedmixture with a polypropylene resin and an amorphous resin having a glasstransition temperature of 120° C. or higher and 250° C. or lower whileheating at 210° C. to 250° C.

Polypropylene Resin

The polypropylene resin is preferably a non-modified polypropylene resinhaving a number average molecular weight in a range of 20,000 or greaterand 90,000 or less. A number average molecular weight of less than20,000 reduces the mechanical strength of the bonded magnet. A numberaverage molecular weight of greater than 90,000 increases the viscosity.

The amount of the polypropylene resin is, for example, in a range of0.05 parts by weight or greater and less than 0.65 parts by weight,preferably 0.2 parts by weight or greater and 0.5 parts by weight orless, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, to improve hot waterresistance.

Amorphous Resin

The amorphous resin to be used is a resin having a glass transitiontemperature of 120° C. or higher with good miscibility with thepolypropylene resin in order to compensate for the low thermal stabilityof the acid-modified polypropylene resin and the polypropylene resin.The resin to be used also has a glass transition temperature of 250° C.or lower in order to keep the molding temperature low to preventoxidative degradation of the rare earth-iron-nitrogen-based magneticpowder. Examples of the amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower includepolycarbonate resins (PC), polyphenylene ether resins (PPE), polyethersulfone resins (PES), polysulfone resins (PSU), polyether imide resins(PEI), and polyarylate resins (PAR). These resins may be used alone orin combinations of two or more. In particular, polyphenylene etherhaving a glass transition temperature higher than 200° C. with a verylow water absorption rate is preferable. The polyphenylene ether may bemodified.

The amount of the amorphous resin is, for example, in a range of 0.1parts by weight or greater and less than 3.23 parts by weight,preferably of 0.3 parts by weight or greater and 2.5 parts by weight orless, particularly preferably of 0.7 parts by weight or greater and 2parts by weight or less, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, to improve hot waterresistance.

The total amount of the polypropylene resin and the amorphous resin is,for example, in a range of 0.35 part by weight or greater and less than3.88 parts by weight, preferably of 0.5 parts by weight or greater and2.5 parts by weight or less, with respect to 100 parts by weight of therare earth-iron-nitrogen-based magnetic powder, to improve hot waterresistance.

Polymer Alloy

In order to improve miscibility with the acid-modified polypropyleneresin, it is preferable to use a polymer alloy containing thepolypropylene resin and the amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower.

The polymer alloy resin containing the amorphous resin and thepolypropylene resin may be produced by any conventionally known methods.For example, when the amorphous resin is polyphenylene ether, a polymeralloy resin may be produced by the following methods: a polypropyleneresin and a polyphenylene ether/polystyrene resin are separatelycombined with a peroxide and maleic anhydride, followed by melt-kneadingusing a single screw kneading extruder or a twin-screw kneading extruderto obtain resins graft-modified with the acid anhydride; diamine isadded to these resins and kneaded again to bond the constituentcomponents by grafting. Alternatively, a compatibilizer is added to apolypropylene resin and a polyphenylene ether/polystyrene alloy resinand kneaded. Examples of the compatibilizer used in the latter caseinclude hydrogenated butadiene/styrene copolymers,styrene-ethylene/butylene-styrene block copolymers,styrene-ethylene/butylene-ethylene block copolymers, andethylene-ethylene/butylene-ethylene block copolymers. The amount of thepolypropylene resin in the polymer alloy is adjusted in a range of, forexample, 10% by mass or greater and 20% by mass or less. The amount ofthe amorphous resin is adjusted in a range of, for example, 50% by massor greater and 70% by mass or less. The polymer alloy resin may be acommercial product, and examples include Xyron EV103 and Xyron T0702(Asahi Kasei Corporation), and Lemalloy PX603Y (Mitsubishi ChemicalCorporation).

Examples of the polyphenylene ether resin includepoly(2,6-dimethyl-1,4-phenylene)ether,poly(2-methyl-6-ethyl-1,4-phenylene)ether,poly(2,6-diethyl-1,4-phenylene)ether,poly(2-methyl-6-n-propyl-1,4-phenylene)ether,poly(2-ethyl-6-n-propyl-1,4-phenylene)ether,poly(2,6-di-n-propyl-1,4-phenylene)ether,poly(2-methyl-6-propyl-1,4-phenylene)ether,poly(2-ethyl-6-isopropyl-1,4-phenylene)ether,poly(2,6-diisopropyl-1,4-phenylene)ether,poly(2-methyl-6-phenyl-1,4-phenylene)ether,poly(2,6-diphenyl-1,4-phenylene)ether,poly(2-methyl-6-chloro-1,4-phenylene)ether,poly(2-methyl-6-hydroxyethyl-1,4-phenylene)ether,poly(2-methyl-6-chloroethyl-1,4-phenylene)ether,poly(2-methyl-6-methoxy-1,4-phenylene)ether,poly(2-methyl-1,4-phenylene)ether, poly(1,4-phenylene)ether, andpoly(2,6-di(p-fluorophenyl)-1,4-phenylene)ether.

The amount of the polymer alloy is, for example, in a range of 0.5 partsby weight or greater and less than 5.38 parts by weight, preferably of 1part by weight or greater and 5 parts by weight or less, with respect to100 parts by weight of the rare earth-iron-nitrogen-based magneticpowder, to improve hot water resistance.

Obtaining Third Kneaded Mixture

This embodiment preferably further includes obtaining a third kneadedmixture by kneading the second kneaded mixture and a polypropylene resinhaving a number average molecular weight of 9,000 or less. The thirdkneaded mixture may be obtained by kneading the second kneaded mixtureand a polypropylene resin having a number average molecular weight of9,000 or less while heating at 210° C. to 250° C.

Polypropylene Resin Having Number Average Molecular Weight of 9,000 orLess

Use of a low molecular weight polypropylene resin having a numberaverage molecular weight of 9,000 or less further improves hot waterresistance. Examples of the low molecular weight polypropylene resininclude Hi-Wax (Mitsui Chemicals, Inc.), Umex and Viscol (Sanyo ChemicalIndustries, Ltd.), and Licocene PP (Clariant).

The amount of the polypropylene resin having a number average molecularweight of 9,000 or less is, for example, in a range of 0.01 part byweight or greater and 3.5 parts by weight or less, preferably of 0.08parts by weight or greater and 3 parts by weight or less, particularlypreferably of 0.7 parts by weight or greater and 2.5 parts by weight orless, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, to improve hot waterresistance.

The polypropylene resin having a number average molecular weight of9,000 or less is more preferably a non-modified polypropylene resin. Useof a non-modified polypropylene resin having a number average molecularweight of 9,000 or less further improves hot water resistance.

Additives

In the steps of obtaining the respective kneaded mixtures, variousadditives may be added, if necessary, such as lubricants, antioxidants,heavy metal deactivators, crystal nucleating agents, flame retardants,plasticizers, ultraviolet absorbers, antistatic agents, colorants, andrelease agents. Among these additives, phenolic or phosphorusantioxidants and/or heavy metal deactivators may be suitably used inorder to alleviate damage to the resin molecules due to severeconditions (e.g. high temperature and high humidity), catalysis byultraviolet light or active metals, or external forces (e.g. shear andfriction), to which the product is exposed during the kneading or bondedmagnet formation processes or during actual use.

Method of Manufacturing Composition for Bonded Magnets According toSecond Embodiment

The manufacturing method according to this embodiment is a method ofmanufacturing a composition for bonded magnets, including: providing arare earth-iron-nitrogen-based magnetic powder having a coat layercontaining a basic group, an acid-modified polypropylene resin, apolypropylene resin, and an amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower; and obtaining akneaded mixture by kneading the rare earth-iron-nitrogen-based magneticpowder having a coat layer containing a basic group, the acid-modifiedpolypropylene resin, the polypropylene resin, and the amorphous resinhaving a glass transition temperature of 120° C. or higher and 250° C.or lower, wherein, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, the amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and the total amount of thepolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight.

In the second embodiment, the rare earth-iron-nitrogen-based magneticpowder having a coat layer containing a basic group and theacid-modified polypropylene resin are kneaded together in order toprovide increased water resistance due to the nature of polypropyleneresins and increased adhesion to the magnetic powder due to associationbetween the basic group and the acid-modified portion. It is alsoconsidered that the polypropylene resin and the amorphous resin are alsokneaded together in order to provide the bonded magnet with hot waterresistance attributable to the polypropylene resin and the amorphousresin, as is the case in the first embodiment.

The kneaded mixture in the second embodiment may be obtained by kneadinga rare earth-iron-nitrogen-based magnetic powder having a coat layercontaining a basic group, an acid-modified polypropylene resin, apolypropylene resin, and an amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower while heating at210° C. to 250° C. Any kneading machine may be used, and examplesinclude single-screw extruders, special single-screw extruders,kneaders, mixing rollers, Banbury mixers, intermeshing type twin-screwextruders, and non-intermeshing type twin-screw extruders. The rareearth-iron-nitrogen-based magnetic powder and the resins, and the amountand other conditions thereof are as described above in the firstembodiment, and detailed descriptions thereof are thus omitted.

The kneaded mixture in the second embodiment preferably further containsa polypropylene resin having a number average molecular weight of 9,000or less which has been provided in advance. The polypropylene resinhaving a number average molecular weight of 9,000 or less and the amountand other conditions thereof are as described above in the firstembodiment, and detailed descriptions thereof are thus omitted.

The composition for bonded magnets according to the second embodimentmay be obtained by cutting the above-described kneaded mixture into anappropriate size after cooling.

Composition for Bonded Magnet According to Third Embodiment

The composition for bonded magnets according to this embodimentincludes: a rare earth-iron-nitrogen-based magnetic powder; anacid-modified polypropylene resin; a polypropylene resin; and anamorphous resin having a glass transition temperature of 120° C. orhigher and 250° C. or lower, wherein, with respect to 100 parts byweight of the rare earth-iron-nitrogen-based magnetic powder, the amountof the acid-modified polypropylene resin is 3.5 parts by weight orgreater and less than 10.4 parts by weight, and the total amount of thepolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight.

In the third embodiment, the presence of the acid-modified polypropyleneresin increases adhesion to the rare earth-iron-nitrogen-based magneticpowder. Further, the presence of the polypropylene resin and theamorphous resin having a glass transition temperature of 120° C. orhigher and 250° C. or lower at a predetermined ratio with respect to themagnetic powder provides water resistance attributable to thepolypropylene resin and heat resistance attributable to the amorphousresin. Overall, this results in improved hot water resistance.

Also in the third embodiment, within the composition for bonded magnets,the acid-modified polypropylene resin tends to be located on the surfaceof the magnetic powder particles due to adhesion of the acid-modifiedgroup of the acid-modified polypropylene resin to the magnetic powder,while the polypropylene resin and the amorphous resin having a glasstransition temperature of 120° C. or higher and 250° C. or lower tend tobe located on the surface of the acid-modified polypropylene resin. Theacid-modified group portion of the acid-modified polypropylene resin,which has polarity, can bind to moisture, but hot water resistance isprovided by the presence of the polypropylene resin and the amorphousresin on the surface of the acid-modified polypropylene resin. The rareearth-iron-nitrogen-based magnetic powder and the resins, and the amountand other conditions thereof are as described above in the firstembodiment, and detailed descriptions thereof are thus omitted.

In view of hot water resistance, the composition for bonded magnetspreferably further contains a polypropylene resin having a numberaverage molecular weight of 9,000 or less. When the number averagemolecular weight is 9,000 or less, such a low molecular weight componenttends to bleed out to the outermost surface of the composition to form askin layer, and tends to be located on the surface of the polypropyleneresin and the amorphous resin. This increases hot water resistance. Thepolypropylene resin having a number average molecular weight of 9,000 orless and the amount and other conditions thereof are as described abovein the first embodiment, and detailed descriptions thereof are thusomitted.

With the use of the composition for bonded magnets, it is possible tomanufacture a bonded magnet having good hot water resistance.Specifically, for example, a bonded magnet may be obtained by heattreating the composition for bonded magnets in an orientation field toalign the easy axes of magnetization (orientation step), followed bypulse magnetization in a magnetizing field (magnetization step).

The heat treatment temperature in the orientation step is preferably,for example, 90° C. or higher and 250° C. or lower, more preferably in arange of 150° C. to 230° C. The magnitude of the orientation field inthe orientation step may be, for example, 720 kA/m. The magnitude of themagnetizing field in the magnetization step may be, for example, 1500 to2500 kA/m.

EXAMPLES

Hereinafter, certain examples of the present invention are described indetail. The details of materials, test methods, and evaluation methodsare described by means of examples, but the present invention is notlimited to these examples, and modifications may be made withoutdeparting from the gist of the present invention.

1. Providing Raw Materials

1-1. Rare Earth-Iron-Nitrogen-Based Magnetic Powder

Surface Treatment Method

An Sm—Fe—N anisotropic magnetic powder (3,000 g) was introduced into amixer, followed by purging with nitrogen. Then, a mixed solution of asilane coupling agent (γ-aminopropyltriethoxysilane) (12 g), ethanol (12g), and ammonia water (6 g) was added by spray to the magnetic powderwith mixing, followed by mixing for one minute and then drying undernitrogen flow at 120° C. for five hours. Thus, an Sm₂Fe₁₇N₃ powderhaving a coupling agent film formed on a silica film (hereinafter,magnetic powder (A)) was obtained.

Average particle size: about 2.8 μm (measured by FSSS method)

Magnetic properties:

Remanence (Br): 12.5 kG

Inherent coercive force (iHc): 16 kOe

Squareness (Hk): 7 kOe

1-2. Acid-Modified Polypropylene Resin (Hereinafter, Resin (A))

Polypropylene Resin:

-   -   Degree of maleic anhydride modification: 1% by weight    -   Number average molecular weight (Mn): about 40,000        1-3. Polypropylene Resin (Hereinafter, Resin (B)) and Amorphous        Resin (Hereinafter, Resin (C))

Polypropylene resin:

-   -   Acid modification: none    -   Number average molecular weight (Mn): about 20,000

Amorphous resin: poly(2,6-dimethyl-1,4-phenylene)ether resin (Tg: about214° C.)

Polyphenylene Ether/Polystyrene/Polypropylene Composite Alloy Resin

Production Method

The resin (B) (15 parts by weight) and astyrene-ethylene/butylene-styrene block copolymer (styrene content: 53%,specific gravity: 0.97) (10 parts by weight) were added to a miscibleresin (100 parts by weight) obtained by kneading the resin (C) and apolystyrene resin at a ratio of 3:1, and they are kneaded using atwin-screw extruder to obtain a polyphenyleneether/polystyrene/polypropylene composite alloy resin (hereinafter,alloy resin (D)).

1-4. Resin (E)

Polypropylene resin (E-1):

-   -   Degree of maleic anhydride modification: 0% by weight    -   Number average molecular weight (Mn): 3,000

Polypropylene resin (E-2):

-   -   Degree of maleic anhydride modification: 0% by weight    -   Number average molecular weight (Mn): 4,000

Polypropylene resin (E-3):

-   -   Degree of maleic anhydride modification: 0% by weight    -   Number average molecular weight (Mn): 9,000

Polypropylene resin (E-4):

-   -   Degree of maleic anhydride modification: about 0.3% by weight    -   Number average molecular weight (Mn): 3,500

Example 1

Manufacturing Composition for Bonded Magnets

The magnetic powder (A), the resin (A), the alloy resin (D), and anantioxidant were introduced into a twin-screw kneading machine suchthat, with respect to 100 parts by weight of the magnetic powder, theamount of the resin (A) was 7.36 parts by weight, the amount of theresin (D) was 3.15 parts by weight, and the amount of the antioxidantwas 0.3 parts by weight. The mixture was kneaded at 220° C. to obtain akneaded mixture. After cooling, the obtained kneaded mixture was cutinto an appropriate size to obtain a composition for bonded magnets.

Molding

The obtained composition for bonded magnets was melted in a cylinder at240° C., and injection-molded in an orientation field of 9 kOe in a moldwhose temperature was adjusted to 90° C. Thus, a cylindrical bondedmagnet (ϕ10/t7) was obtained. The magnet was imparted with magneticproperties by pulse magnetization in a magnetizing field of 60 kOe.

Hot Water Resistance Evaluation

The magnetized bonded magnet was placed with water in apressure-resistant vessel and subjected to a pressure cooker test (PCT)(121° C./2 atm/450 hr) to evaluate hot water resistance. For the hotwater resistance evaluation, the total flux of the bonded magnet wasmeasured before and after the PCT test using a flux meter, and the hotwater resistance was evaluated based on the irreversible demagnetizationratio [(total flux of bonded magnet after 450-hour PCT)/(total flux ofbonded magnet before 450-hour PCT)×100)].

Example 2

Manufacturing Composition for Bonded Magnets

The magnetic powder (A), the resin (A), the alloy resin (D), the resin(E-1), and an antioxidant were introduced into a twin-screw kneadingmachine such that, with respect to 100 parts by weight of the magneticpowder, the amount of the resin (A) was 7.29 parts by weight, the amountof the resin (D) was 3.15 parts by weight, the amount of the resin (E-1)was 0.08 parts by weight, and the amount of the antioxidant was 0.3parts by weight. The mixture was kneaded at 220° C. to obtain a kneadedmixture. After cooling, the obtained kneaded mixture was cut into anappropriate size to obtain a composition for bonded magnets.

Molding

A bonded magnet was produced in the same manner as in Example 1, andevaluated for hot water resistance.

Comparative Example 1

The magnetic powder (A) and a 12 nylon (PA12) resin (weight averagemolecular weight Mw: 12,000) were kneaded while heating at 210° C. usinga twin-screw kneading machine such that, with respect to 100 parts byweight of the magnetic powder, the amount of the PA12 resin was 8.3parts by weight and the amount of an antioxidant was 0.3 parts byweight. After cooling, the obtained kneaded mixture was cut into anappropriate size to obtain a composition for bonded magnets.

Molding

The obtained composition for bonded magnets was melted in a cylinder at230° C., and injection-molded in an orientation field of 9 kOe in a moldwhose temperature was adjusted to 90° C. Thus, a cylindrical bondedmagnet (ϕ10/t7) was obtained. The magnet was imparted with magneticproperties by pulse magnetization in a magnetizing field of 60 kOe.

Hot Water Resistance Evaluation

The hot water resistance of the obtained bonded magnet was evaluated inthe same manner as in Example 1.

Comparative Example 2

The magnetic powder (A) and a polyphenylene sulfide (PPS) resin (linear;weight average molecular weight Mw: 20,000) were kneaded while heatingat 300° C. using a twin-screw kneading machine such that the amount ofthe PPS resin was 14 parts by weight with respect to 100 parts by weightof the magnetic powder. After cooling, the obtained kneaded mixture wascut into an appropriate size to obtain a composition for bonded magnets.

Molding

The obtained compound was melted in a cylinder at 320° C., andinjection-molded in an orientation field of 9 kOe in a mold whosetemperature was adjusted to 150° C. Thus, a cylindrical bonded magnet(ϕ0/t7) was obtained. The magnet was imparted with magnetic propertiesby pulse magnetization in a magnetizing field of 60 kOe.

Hot Water Resistance Evaluation

The hot water resistance of the obtained bonded magnet was evaluated inthe same manner as in Example 1.

Examples 3 to 13 and Comparative Examples 3 and 4

Bonded magnets were produced in the same manner as in Example 1 orExample 2, except that, with respect to 100 parts by weight of themagnetic powder (A), the amounts of the resin (A) and the alloy resin(D) were as indicated in Table 1 and that the type of resin (E) and itsamount (with respect to 100 parts by weight of the magnetic powder (A))were as indicated in Table 1. Then, their hot water resistance wasevaluated. In addition, the alloy resin (D) in Example 13 or ComparativeExample 4 was provided with a ratio shown in Table 1 by the same methodas described above for the alloy resin.

TABLE 1 Alloy resin Resin (A) Resin (B) Resin (C) (D) Resin (E) PA12resin PPS resin Demagnetization Parts by Parts by Parts by Parts byParts by Parts by Parts by ratio weight weight weight B + C weight Typeweight weight weight % Example 1 7.36 0.38 1.89 2.27 3.15 — — — — 26.3Example 2 7.29 0.38 1.89 2.27 3.15 E-1 0.08 — — 26 Example 3 7.14 0.381.89 2.27 3.15 E-1 0.23 — — 20.5 Example 4 6.99 0.38 1.89 2.27 3.15 E-10.38 — — 22 Example 5 6.62 0.38 1.89 2.27 3.15 E-1 0.75 — — 16.1 Example6 5.87 0.38 1.89 2.27 3.15 E-1 1.5  — — 15.4 Example 7 5.13 0.38 1.892.27 3.15 E-1 2.25 — — 16.8 Eaxmple 8 6.62 0.38 1.89 2.27 3.15 E-2 0.75— — 17.2 Example 9 6.62 0.38 1.89 2.27 3.15 E-3 0.75 — — 15 Example 107.14 0.38 1.89 2.27 3.15 E-4 0.23 — — 26.7 Example 11 6.99 0.38 1.892.27 3.15 E-4 0.38 — — 25.3 Example 12 6.62 0.38 1.89 2.27 3.15 E-4 0.75— — 26.2 Example 13 9.3 0.12 0.62 0.74 1.03 — — — — 25.2 Comparative — —— — — — 8.3 — 52 Example 1 Comparative — — — — — — — 14 29.3 Examlpe 2Comparative 10.4 — — — — — — — 38.4 Example 3 Coparative 5.38 0.65 3.233.88 5.38 — — — — 31.6 Example 4

Example 14

Obtaining First Kneaded Mixture

The magnetic powder (A), the resin (A), and an antioxidant areintroduced into a twin-screw kneading machine through its first feedersuch that, with respect to 100 parts by weight of the magnetic powder(A), the amount of the resin (A) is 6.62 parts by weight and the amountof the antioxidant is 0.3 parts by weight. The mixture is kneaded at220° C. to obtain a first kneaded mixture.

Obtaining Second Kneaded Mixture

The alloy resin (D) is introduced into the twin-screw kneading machinethrough its second feeder such that, with respect to 100 parts by weightof the magnetic powder (A), the amount of the alloy resin (D) is 3.15parts by weight (with respect to the magnetic powder (A), the amount ofthe resin (B) is 0.38 parts by weight and the amount of the resin (C) is1.89 parts by weight), and then kneaded with the first kneaded mixtureat 220° C. to obtain a second kneaded mixture.

Obtaining Third Kneaded Mixture

The resin (E-3) is introduced into the twin-screw kneading machinethrough its third feeder such that the amount of the resin (E-3) is 0.75parts by weight with respect to 100 parts by weight of the magneticpowder (A), and then kneaded with the second kneaded mixture at 220° C.to obtain a third kneaded mixture. After cooling, the obtained thirdkneaded mixture is cut into an appropriate size to obtain a compositionfor bonded magnets.

Molding and Hot Water Resistance Evaluation

A bonded magnet was produced in the same manner as in Example 1 toevaluate hot water resistance.

Table 1 shows the relationships between the composition and thedemagnetization ratio of the bonded magnets obtained above. FIG. 1 showsthe relationships between the demagnetization ratio and the elapsed timein the PCT test. As shown in FIG. 1, in Comparative Example 1, thedemagnetization after one-hour PCT (hereinafter, initialdemagnetization) was small, but eventually the magnet was greatlydemagnetized. This is probably because, since the moisture-absorbing PAresin was used, the magnetic powder was degraded by reaction with themoisture that penetrated into the magnet over time. In ComparativeExample 2, the initial demagnetization was large, the demagnetizationproceeded with time, and eventually the magnet was greatly demagnetized.This is probably because the kneading temperature and the bonded magnetmolding temperature had to be set to 300° C. due to the high viscosityof the PPS resin, and therefore the magnetic powder was oxidativelydegraded at such high temperatures. In Comparative Example 3, theinitial demagnetization was small, but eventually the magnet was greatlydemagnetized, and thus the same tendency as the 12 nylon magnet wasobserved. This is probably because, since the acid-modifiedpolypropylene resin alone was used, the heat resistance was insufficientand the magnet was softened at high temperatures, thus allowingpenetration and diffusion of moisture into the magnet. The results inComparative Example 4 are probably because, since the amount of the acidmodification polypropylene resin relative to the amount of the alloyresin was small, the water resistance was insufficient, thus allowingpenetration and diffusion of moisture into the magnet. In contrast, inExamples 1 to 13, the initial demagnetization and the finaldemagnetization were both suppressed. This is probably because thekneading temperature and the molding temperature were reduced to 240°C., and also because the resins were incorporated in predeterminedamounts to provide the bonded magnet with appropriate hot waterresistance. Moreover, Example 14, which had the same composition as inExample 9, would be expected to show a demagnetization ratio equal to orlower than that in Example 9, as described for the first embodiment.

FIG. 2 shows a graph of amount of the resin (E-1) versus irreversiblemagnetization ratio after a pressure cooker test (121° C./2 atm/450 hr).The results show that the amount of the resin (E-1) able to effectivelyreduce the demagnetization ratio of the magnet was 0.2 parts by weightor greater. The demagnetization ratio was found to be reducedparticularly when the amount of the resin (E-1) was 0.75 parts by weightor greater and 1.75 parts by weight or less.

FIG. 3 shows a graph of degree of maleic anhydride modification versusirreversible demagnetization ratio after a pressure cooker test (121°C/2 atm/200 hr) of bonded magnets produced in the same manner as inExample 1 but replacing the resin (A) with maleic anhydride-modifiedpolypropylene resins having varying degrees of modification ranging from0 to 2.8% by weight (0, 0.14, 0.35, 0.7, 1, 1.4, 1.75, and 2.8% byweight). The results show that the degree is preferably 0.2% by weightor greater and 2.8% by weight or less, more preferably 0.35% by weightor greater and 1.4% by weight or less, particularly preferably 0.7% byweight or greater and 1.25% by weight or less.

The present invention provides compositions for bonded magnets that maybe suitably used in magnet components for motors, sensors, or actuatorswhich are to be exposed to high-temperature, high-humidity environmentsor hot water.

What is claimed is:
 1. A method of manufacturing a composition forbonded magnets, the method comprising: obtaining a first kneaded mixtureby kneading a rare earth-iron-nitrogen-based magnetic powder and anacid-modified polypropylene resin; and obtaining a second kneadedmixture by kneading the first kneaded mixture with a first polypropyleneresin and a polyphenylene ether resin, wherein, with respect to 100parts by weight of the rare earth-iron-nitrogen-based magnetic powder,an amount of the acid-modified polypropylene resin is 3.5 parts byweight or greater and less than 10.4 parts by weight, and a total amountof the first polypropylene resin and the polyphenylene ether resin is0.35 part by weight or greater and less than 3.88 parts by weight. 2.The method of manufacturing a composition for bonded magnets accordingto claim 1, wherein obtaining the second kneaded mixture compriseskneading the first kneaded mixture with a polymer alloy containing thefirst polypropylene resin and the polyphenylene ether resin.
 3. Themethod of manufacturing a composition for bonded magnets according toclaim 1, wherein the rare earth-iron-nitrogen-based magnetic powder hasa coat layer containing a basic group.
 4. The method of manufacturing acomposition for bonded magnets according to claim 1, wherein theacid-modified polypropylene resin has a degree of acid modificationrelative to polypropylene of 0.1% by weight or greater and 5% by weightor less.
 5. The method of manufacturing a composition for bonded magnetsaccording to claim 1, the method further comprising obtaining a thirdkneaded mixture by kneading the second kneaded mixture and a secondpolypropylene resin having a number average molecular weight of 9,000 orless.
 6. The method of manufacturing a composition for bonded magnetsaccording to claim 5, wherein the second polypropylene resin having anumber average molecular weight of 9,000 or less comprises anon-modified polypropylene resin.
 7. The method of manufacturing acomposition for bonded magnets according to claim 5, wherein an amountof the second polypropylene resin having a number average molecularweight of 9,000 or less is 0.01 part by weight or greater and 3.5 partsby weight or less with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder.
 8. A composition for bondedmagnets, comprising: a rare earth-iron-nitrogen-based magnetic powder;an acid-modified polypropylene resin; a first polypropylene resin; and apolyphenylene ether resin, wherein, with respect to 100 parts by weightof the rare earth-iron-nitrogen-based magnetic powder, an amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and a total amount of the firstpolypropylene resin and the amorphous resin polyphenylene ether resin is0.35 part by weight or greater and less than 3.88 parts by weight. 9.The composition for bonded magnets according to claim 8, wherein theacid-modified polypropylene resin is present on a surface of the rareearth-iron-nitrogen-based magnetic powder, and the first polypropyleneresin and the polyphenylene ether resin are present on a surface of theacid-modified polypropylene resin.
 10. The composition for bondedmagnets according to claim 8, wherein the first polypropylene resin andthe polyphenylene ether resin form a polymer alloy.
 11. The compositionfor bonded magnets according to claim 8, wherein the rareearth-iron-nitrogen-based magnetic powder has a coat layer containing abasic group.
 12. The composition for bonded magnets according to claim8, wherein the acid-modified polypropylene resin has a degree of acidmodification relative to polypropylene of 0.1% by weight or greater and5% by weight or less.
 13. The composition for bonded magnets accordingto claim 8, further comprising a second polypropylene resin having anumber average molecular weight of 9,000 or less.
 14. The compositionfor bonded magnets according to claim 13, wherein the secondpolypropylene resin having a number average molecular weight of 9,000 orless is present on a surface of the first polypropylene resin and asurface of the polyphenylene ether resin.
 15. The composition for bondedmagnets according to claim 13, wherein the second polypropylene resinhaving a number average molecular weight of 9,000 or less comprises anon-modified polypropylene resin.
 16. The composition for bonded magnetsaccording to claim 13, wherein an amount of the second polypropyleneresin having a number average molecular weight of 9,000 or less is 0.01part by weight or greater and 3.5 parts by weight or less with respectto 100 parts by weight of the rare earth-iron-nitrogen-based magneticpowder.
 17. A method of manufacturing a composition for bonded magnets,the method comprising: providing a rare earth-iron-nitrogen-basedmagnetic powder having a coat layer containing a basic group, anacid-modified polypropylene resin, a first polypropylene resin, and anamorphous resin having a glass transition temperature of 120° C. orhigher and 250° C. or lower; and obtaining a kneaded mixture by kneadingthe rare earth-iron-nitrogen-based magnetic powder having a coat layercontaining a basic group, the acid-modified polypropylene resin, thefirst polypropylene resin, and the amorphous resin having a glasstransition temperature of 120° C. or higher and 250° C. or lower,wherein, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, an amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and a total amount of the firstpolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight.
 18. The method ofmanufacturing a composition for bonded magnets according to claim 17,wherein the method comprises: further providing a second polypropyleneresin having a number average molecular weight of 9,000 or less; andobtaining a kneaded mixture by kneading the rareearth-iron-nitrogen-based magnetic powder having a coat layer containinga basic group, the acid-modified polypropylene resin, the firstpolypropylene resin, the amorphous resin having a glass transitiontemperature of 120° C. or higher and 250° C. or lower, and the secondpolypropylene resin having a number average molecular weight of 9,000 orless.
 19. A method of manufacturing a composition for bonded magnets,the method comprising: obtaining a first kneaded mixture by kneading arare earth-iron-nitrogen-based magnetic powder and an acid-modifiedpolypropylene resin; and obtaining a second kneaded mixture by kneadingthe first kneaded mixture with a first polypropylene resin and anamorphous resin having a glass transition temperature of 120° C. orhigher and 250° C. or lower, wherein, with respect to 100 parts byweight of the rare earth-iron-nitrogen-based magnetic powder, an amountof the acid-modified polypropylene resin is 3.5 parts by weight orgreater and less than 10.4 parts by weight, and a total amount of thefirst polypropylene resin and the amorphous resin is 0.35 part by weightor greater and less than 3.88 parts by weight, and wherein the rareearth-iron-nitrogen-based magnetic powder has a coat layer containing abasic group.
 20. A composition for bonded magnets, comprising: a rareearth-iron-nitrogen-based magnetic powder; an acid-modifiedpolypropylene resin; a first polypropylene resin; and an amorphous resinhaving a glass transition temperature of 120° C. or higher and 250° C.or lower, wherein, with respect to 100 parts by weight of the rareearth-iron-nitrogen-based magnetic powder, an amount of theacid-modified polypropylene resin is 3.5 parts by weight or greater andless than 10.4 parts by weight, and a total amount of the firstpolypropylene resin and the amorphous resin is 0.35 part by weight orgreater and less than 3.88 parts by weight, and wherein the rareearth-iron-nitrogen-based magnetic powder has a coat layer containing abasic group.